Very low temperature refrigerator

ABSTRACT

An inverter ( 22 ) is provided between a power source ( 20 ) and a suction/discharge valve driving motor ( 14 ) that controls cycle time of suction and discharge of a refrigerator unit ( 10 ). An output frequency of the inverter ( 22 ) is controlled in accordance with output of a sensor ( 24 ) that detects temperature of a thermal load portion ( 11 ) of the refrigerator unit ( 10 ). This enables temperature adjustment of individual refrigerators with a highly reliable method without using an electric heater.

TECHNICAL FIELD

The present invention relates to a cryogenic refrigerator, particularlyto a cryogenic refrigerator capable of performing temperature adjustmentand suitable for use with cryopump, superconductive magnet, cryogenicmeasuring apparatus, simple liquefaction apparatus or the like.

BACKGROUND ART

In general, a cryogenic refrigerator includes: an expansion typerefrigerator unit accommodating a thermal accumulation material and hasan expansion chamber located within the refrigerator; and a compressorunit containing a compressor main body. The refrigerator unit isinstalled within an apparatus or a container which is to be cooled to anextremely low temperature. Then, a high pressure refrigerant gasobtained through the compressor unit is fed to the refrigerator unitwhere the high pressure refrigerant gas is cooled by the thermalaccumulation material and then expanded, followed by carrying out afurther cooling step. Subsequently, a low pressure refrigerant gas isreturned to the compressor unit, thereby forming a refrigerating cycleand thus obtaining an extremely low temperature by repeating suchrefrigerating cycle.

Conventionally, when such a refrigerator is used to perform temperatureadjustment, an electric heater is provided in the refrigerator unit soas to introduce a thermal load and thus perform temperature adjustment.

However, since the heater is used in an extremely low temperatureenvironment, its reliability is low, resulting in a low insulation whichcauses an electric leak and hence some troubles such as an emergencyshut down due to such an electric leak.

Further, as another method, as recited in Japanese Patent Laid-OpenPublication No. 2000-121192, it is conceivable that an inverter controlsthe rotation speed of a compressor main body to adjust a gas amount soas to effect temperature adjustment. Although this method is effectivewhen a single refrigerator unit is operated by a single compressor unit,when a plurality of refrigerator units are operated by one or morecompressor units, there had been a problem that it was impossible toperform the temperature adjustment of the respective refrigerator units.

Moreover, in the case where a plurality of refrigerator units areoperated by one or more compressor units, since the valve timing at thestart of each refrigerator unit is not changed, there had been a problemthat an irregularity occurred among the flow rates of gases flowing intothe respective refrigerator units (when intake timings got overlapped,more gas would flow to refrigerator units whose intakes occurredearlier), causing an irregularity among the refrigerating abilities ofthe refrigerator units.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished to solve the above-describedconventional problems, and its first object is to make it possible toadjust a temperature by a temperature control mechanism provided in aroom temperature area.

A second object of the present invention is to eliminate an irregularityamong refrigerator units when a plurality of refrigerator units areoperated by one or more compressor units.

A third object of the invention is to reduce power consumption.

The present invention has achieved the above first object by comprising:in a cryogenic refrigerator, means, which is provided between a powersource and a motor for driving an intake/exhaust valve managing anintake/exhaust cycle time of a refrigerator unit, for varying afrequency of the motor for driving the intake/exhaust valve; atemperature sensor for detecting a temperature of a thermal load unit ofthe refrigerator unit; and a controller for controlling the means forvarying the frequency of the motor for driving the intake/exhaust valvein accordance with an output signal of the temperature sensor.

Further, in the case where a plurality of refrigerator units areoperated by one or more compressor units, refrigerator units using theabove-mentioned means are constituted, thereby achieving the abovesecond object.

Moreover, the present invention has achieved the above third object byusing a compressor unit in a cryogenic refrigerator, which compressorunit comprises: means, which is provided between a power source and acompressor main body motor of the compressor unit, for varying afrequency of the compressor main body motor; a high pressure sensorattached to a high pressure refrigerant pipe connecting an outlet of thecompressor main body with a refrigerant supply port of the refrigeratorunit; a low pressure sensor attached to a low pressure refrigerant pipeconnecting an inlet of the compressor main body with a refrigerantdischarge outlet of the refrigerator unit; a controller for controllingthe means for varying the frequency of the compressor main body motor inaccordance with output signals of the high pressure sensor and the lowpressure sensor, and by constituting the refrigerator using a pluralityof the refrigerator units and one or more of the compressor units.

Furthermore, the present invention has achieved the above third objectby using a compressor unit in a cryogenic refrigerator, which compressorunit comprises: means, which is provided between a power source and acompressor main body motor of the compressor unit, for varying afrequency of the compressor main body motor; a differential pressuresensor provided between a high pressure refrigerant pipe connecting anoutlet of the compressor main body with a refrigerant supply port of therefrigerator unit and a low pressure refrigerant pipe connecting aninlet of the compressor main body with a refrigerant discharge outlet ofthe refrigerator unit; a controller for controlling the means forvarying the frequency of the compressor main body motor in accordancewith an output signal of the differential pressure sensor, and byconstituting the refrigerator using a plurality of the refrigeratorunits and one or more of the compressor units.

The present invention further provides a cryopump characterized byincluding the refrigerator unit or the cryogenic refrigerator, therebyachieving the above first object as well as the above second and thirdobjects.

The present invention further provides a cryopump characterized bycomprising: a temperature sensor for detecting a temperature at anyoptional position of a cryopanel of the cryopump; and a controller forcontrolling the means for varying the frequency of the motor driving theintake/exhaust valve managing the intake/exhaust cycle time of therefrigerator unit in accordance with an output of the temperaturesensor, thereby achieving the above first object as well as the abovesecond and third objects.

In addition, the present invention provides a superconductive magnetcharacterized by including the above-mentioned refrigerator unit or theabove-mentioned cryogenic refrigerator, thereby achieving the abovefirst object as well as the above second and third objects.

The present invention further provides a superconductive magnetcharacterized by comprising: a temperature sensor for detecting atemperature of any optional position of the superconductive magnet; anda controller for controlling the means for varying the frequency of themotor driving the intake/exhaust valve managing the intake/exhaust cycletime of the refrigerator unit in accordance with an output of thetemperature sensor, thereby achieving the above first object as well asthe above second and third objects.

In addition, the present invention provides a cryogenic measuringapparatus characterized by including the above-mentioned refrigeratorunits or the above-mentioned cryogenic refrigerators, thereby achievingthe above first object as well as the above second and third objects.

The present invention further provides a cryogenic measuring apparatuscharacterized by comprising a temperature sensor for detecting atemperature of any optional position of the cryogenic measuringapparatus; and a controller for controlling the means for varying thefrequency of the motor driving the intake/exhaust valve managing theintake/exhaust cycle time of the refrigerator unit in accordance with anoutput of the temperature sensor, thereby achieving the above firstobject as well as the above second and third objects.

In addition, the present invention provides a simple liquefactionapparatus characterized by comprising the above-mentioned refrigeratorunit or the above-mentioned cryogenic refrigerator, thereby achievingthe above first object as well as the above second and third objects.

The present invention further provides a simple liquefaction apparatuscharacterized by comprising a temperature sensor for detecting atemperature of any optional position of the simple liquefactionapparatus; and a controller for controlling the means for varying thefrequency of the motor driving the intake/exhaust valve managing theintake/exhaust cycle time of the refrigerator unit in accordance with anoutput of the temperature sensor, thereby achieving the above firstobject as well as the above second and third objects.

The present invention further provides a simple liquefaction apparatuscharacterized by comprising liquid-level detecting means within a liquidstorage container of the simple liquefaction apparatus; and a controllerfor controlling means for varying a frequency of a motor driving anintake/exhaust valve managing a intake/exhaust cycle time of arefrigerator unit in accordance with an output of the liquid leveldetecting means, thereby achieving the above first object as well as theabove second and third objects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the constitution of a first embodimentof a cryogenic refrigerator according to the present invention;

FIG. 2 is a chart showing a comparison between an effect of the firstembodiment and a prior art;

FIG. 3 is a pipeline diagram showing the constitution of a secondembodiment of the present invention;

FIG. 4 is a pipeline diagram showing the constitution of a thirdembodiment of the present invention;

FIG. 5 is a pipeline diagram showing the constitution of a fourthembodiment of the present invention;

FIG. 6 is a schematic constitutional view of a cryopump representing afifth embodiment of the present invention;

FIG. 7 is a schematic constitutional view of a superconductive magnetrepresenting a sixth embodiment of the present invention;

FIG. 8 is a schematic constitutional view of a cryogenic measurementapparatus representing a seventh embodiment of the present invention;

FIG. 9 is a schematic constitutional view of a simple liquefactionapparatus representing an eighth embodiment of the present invention;and

FIG. 10 is a schematic constitutional view showing a case in whichliquid-level indicators are used in the simple liquefaction apparatuses,representing a ninth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings.

A first embodiment of the present invention, as shown in FIG. 1, isformed by applying the present invention to the case where thetemperature of a first-stage low-temperature unit 11 of a refrigeratorunit 10 of a second-stage G-M (Gifford McMahon) cycle refrigerator isadjusted. In detail, the first embodiment comprises an inverter 22provided between a power source 20 and a motor 14 for driving anintake/exhaust valve which manages an intake/exhaust cycle time of therefrigerator unit 10, a temperature sensor 24 for detecting thetemperature of the first-stage low-temperature unit 11 which is athermal load portion of the refrigerator unit 10, and a controller 26for feedback controlling the output frequency of the inverter 22 inresponse to the output of the temperature sensor 24. In the figure, thereference numeral 12 represents a second-stage low-temperature unit ofthe refrigerator unit 10.

In the present embodiment, the output frequency of the inverter 22 isfeedback controlled by the controller 26 in response to the temperatureof the first-stage low-temperature unit 11 detected by the temperaturesensor 24, thereby the intake/exhaust cycle time of the refrigeratorunit 10 is adjusted by the intake/exhaust valve driving motor 14.Accordingly, when the temperature of the first-stage low-temperatureunit 11 is lower than a target value, it is possible to increase thetemperature of the first-stage low-temperature unit 11 by increasing theintake/exhaust cycle time of the refrigerator. On the other hand, whenthe temperature of the first-stage low-temperature unit 11 is higherthan the target value, it is possible to lower the temperature of thefirst-stage low-temperature unit 11 by reducing the intake/exhaust cycletime of the refrigerator.

FIG. 2 shows a variation of the temperature (referred to as first-stagetemperature) of the first-stage low-temperature unit when a load ischanged to 15 W, 5 W, and 0 W. When the rotation speed of a refrigeratoris fixed at 72 rpm as in the prior art, the first-stage temperaturevaries from 100.9 K to 65 K, 45 K as a load decreases, as shown by abroken line in the graph. Different from this, according to the presentinvention, where the rotation speed of the refrigerator has been reducedto 42 rpm when a load is 5 W, and 30 rpm when a load is 0 W, thefirst-stage temperature can be maintained at a substantially constantvalue of 100 K, as shown by a solid line in the graph.

Next, a second embodiment of the present invention will be described.

The present embodiment, as shown in FIG. 3, is formed by applying thepresent invention to the case where a single compressor unit 30 is usedto run refrigerator units 10A, 10B, and 10C of three second-stage G-Mcycle refrigerators. Similar to the first embodiment, the refrigeratorunits 10A, 10B, and 10C are provided with inverters 22A, 22B, and 22C,temperature sensors 24A, 24B, and 24C, as well as controllers 26A, 26B,and 26C, respectively.

In the present embodiment, since each refrigerator unit can control anintake/exhaust cycle time in a manner such that the temperature of thefirst-stage low-temperature unit can reach a target value, it ispossible to eliminate an irregularity among these refrigerator units.

Next, a third embodiment of the present invention will be described.

The present embodiment, as shown in FIG. 4, is formed by applying thepresent invention to the case where a single compressor unit 30 is usedto run refrigerator units 10A, 10B, and 10C of three second-stage G-Mcycle refrigerators. Similar to the first embodiment, the refrigeratorunits 10A, 10B, and 10C are provided with inverters 22A, 22B, and 22C,temperature sensors 24A, 24B, and 24C, as well as controllers 26A, 26B,and 26C, respectively.

The present embodiment further comprises: a second inverter 40 providedbetween the power source 20 and the compressor unit 30; pressure sensors42 and 44 provided on a high-pressure gas line 32 and a low-pressure gasline 34 both serving as actuation gas pipelines and connecting thecompressor unit 30 with the respective refrigerator units 10A, 10B, and10C; and a second controller 46 which calculates a differential pressurebetween the high-pressure gas and the low-pressure gas in accordancewith the output signals of the pressure sensors 42 and 44, and controlsan output frequency of the second inverter 40, thereby adjusting therotation speed of the compressor as well as the differential pressure.

In the present embodiment, since the refrigerating abilities of therefrigerators depend on the differential pressure between thehigh-pressure gas and the low-pressure gas, the differential pressure isfirst controlled at a constant value by the outputs of the pressuresensors 42 and 44. At this time, since the refrigerator units, whichhave small thermal loads, are configured such that their intake/exhaustcycle times are extended by the inverters 22A, 22B, or 22C, it ispossible to reduce the gas flow rate and adjust the gas to a requiredtemperature. At this time, although the amounts of gases flowing intothe refrigerator units will decrease and thus the differential pressuretrends to increase, since the rotation speed of the compressor 30 willdecrease due to the inverter 40 so that the differential pressure can bekept constant, it is possible to reduce an entire power consumption.

According to the present embodiment, it is possible not only to adjustthe temperatures of the respective refrigerators by the inverters 22A,22B, and 22C provided in the respective refrigerator units and toeliminate an irregularity among the refrigerator units, but also toreduce power consumption by the second inverter 40 provided in thecompressor unit 30.

Next, a fourth embodiment of the present invention will be described.

The present embodiment, as shown in FIG. 5, is formed by applying thepresent invention to the case where a single compressor unit 30 is usedto run refrigerator units 10A, 10B, and 10C of three second-stage G-Mcycle refrigerators. Similar to the first embodiment, the refrigeratorunits 10A, 10B, and 10C are provided with inverters 22A, 22B, and 22C,temperature sensors 24A, 24B, and 24C, as well as controllers 26A, 26B,and 26C, respectively.

The present embodiment is further provided with: a second inverter 40provided between the power source 20 and the compressor unit 30; adifferential pressure sensor 48 provided between a high-pressure gasline 32 and a low-pressure gas line 34 both serving as actuation gaspipelines and connecting the compressor unit 30 with the refrigeratorunits 10A, 10B, and 10C; and a second controller 46 which controls theoutput frequency of the second inverter 40 in accordance with the outputsignal of the differential pressure sensor 48, thereby adjusting therotation speed of the compressor unit 30 as well as the differentialpressure.

In the present embodiment, since the refrigerating abilities of therefrigerating machines depend on the differential pressure between thehigh-pressure gas and the low-pressure gas, the differential pressure isfirst controlled at a constant value by the output of the differentialpressure sensor 48. At this time, since the refrigerator units, whichhave small thermal loads, are configured such that their intake/exhaustcycle times are extended by the inverters 22A, 22B, or 22C, it ispossible to reduce the gas flow rate and adjust the gas to a requiredtemperature. At this time, although the amounts of gases flowing intothe refrigerator units will decrease and thus the differential pressuretrends to increase, since the rotation speed of the compressor 30 willdecrease due to the inverter 40 so that the differential pressure can bekept constant, it is possible to reduce an entire power consumption.

According to the present embodiment, it is possible not only to adjustthe temperatures of the respective refrigerators by the inverters 22A,22B, and 22C provided in the respective refrigerator units and toeliminate an irregularity among the refrigerator units, but also toreduce power consumption by the second inverter 40 provided in thecompressor unit 30.

FIG. 6 shows a fifth embodiment in which the present invention has beenapplied to cryopumps. The drawing actually shows an application of thethird embodiment of the invention to cryopumps, with the same portionshaving the same constitutions and functions as those shown in FIG. 4being represent by the same reference numerals, and same descriptionsbeing omitted.

In the present embodiment, the reference numerals 50A, 50B, and 50Crepresent pump containers to which the refrigerator units 10A, 10B, and10C are attached, while 52A, 52B, and 52C represent chambers to beevacuated in a semiconductor manufacturing apparatus, for example. Thetemperature sensors 24A, 24B, and 24C are not absolutely necessary to beattached to first-stage or second-stage thermal-load portions of therefrigerator units, but can be attached to any desired positions ofcryopanels of the cryopumps.

According to the present invention, as described in the thirdembodiment, it is possible not only to adjust the temperatures of therespective refrigerators by the inverters 22A, 22B, and 22C provided inthe respective refrigerator units and to eliminate an irregularity amongthe refrigerator units, but also to reduce power consumption by thesecond inverter 40 provided in the compressor unit 30.

Incidentally, although in the present embodiment the cryopumps and therefrigerator units are combined with each other in one-to-one relation,it is also possible for the present embodiment to be applied to a systemin which a plurality of refrigerator units are used with a singlecryopump. Moreover, it is possible to apply herein the first embodiment,the second embodiment, and the fourth embodiment.

FIG. 7 shows a sixth embodiment in which the present invention has beenapplied to superconductive magnets. The drawing actually shows anapplication of the third embodiment of the invention to thesuperconductive magnets, with the same portions having the sameconstitutions and functions as those shown in FIG. 4 being represent bythe same reference numerals, and same descriptions being omitted.

In the present embodiment, the reference numerals 60A, 60B, and 60Crepresent superconductive magnets to which the refrigerator units 10A,10B, and 10C are attached, while 62A, 62B, and 62C represent, forexample, nuclear magnetic resonance imaging (MRI) apparatuses. Thetemperature sensors 24A, 24B, and 24C are not absolutely necessary to beattached to first-stage or second-stage thermal-load portions of therefrigerator units, but can be attached to any desired positions of thesuperconductive magnets.

According to the present embodiment, as described in the thirdembodiment, it is possible not only to adjust the temperatures of therespective refrigerators by the inverters 22A, 22B, and 22C provided inthe respective refrigerator units and to eliminate an irregularity amongthe refrigerator units, but also to reduce power consumption by thesecond inverter 40 provided in the compressor unit 30.

Incidentally, although in the present embodiment the superconductivemagnets and the refrigerator units are combined with each other inone-to-one relation, it is also possible for the present embodiment tobe applied to a system in which a plurality of refrigerator units areused with a single superconductive magnet. Moreover, it is possible toapply herein the first embodiment, the second embodiment, and the fourthembodiment.

Here, although the above description has described MRI used in medicalfield, the present invention can also be applied to superconductivemagnet (such as MCZ) used in a non-medical field.

FIG. 8 shows a seventh embodiment in which the present invention hasbeen applied to cryogenic measuring apparatuses. The drawing actuallyshows an application of the third embodiment of the invention tocryogenic measuring apparatuses, with the same portions having the sameconstitutions and functions as those shown in FIG. 4 being represent bythe same reference numerals, and same descriptions being omitted.

In the present embodiment, the reference numerals 70A, 70B, and 70Crepresent cryogenic measuring apparatuses (for example, an X-raydiffraction measuring apparatus, a light-transmission measuringapparatus, a photoluminescence measuring apparatus, a superconductormeasuring apparatus, a Hall-effect measuring apparatus, etc.) to whichthe refrigerator units 10A, 10B, and 10C are attached. The temperaturesensors 24A, 24B, and 24C are not absolutely necessary to be attached tofirst-stage or second-stage thermal-load portions of the refrigeratorunits, but can be attached to any desired positions of the extremely lowtemperature measuring apparatuses.

According to the present embodiment, as described in the thirdembodiment, it is possible not only to adjust the temperatures of therespective refrigerators by the inverters 22A, 22B, and 22C provided inthe respective refrigerator units and to eliminate an irregularity amongthe refrigerator units, but also to reduce power consumption by thesecond inverter 40 provided in the compressor unit 30.

Incidentally, although in the present embodiment the cryogenic measuringapparatuses and the refrigerator units are combined with each other inone-to-one relation, it is also possible for the present embodiment tobe applied to a system in which a plurality of refrigerator units areused with a single cryogenic measuring apparatus. Moreover, it ispossible to apply herein the first embodiment, the second embodiment,and the fourth embodiment.

FIG. 9 shows an eighth embodiment in which the present invention hasbeen applied to simple liquefaction apparatuses. The drawing actuallyshows an application of the third embodiment of the invention to simpleliquefaction apparatuses, with the same portions having the sameconstitutions and functions as those shown in FIG. 4 being represent bythe same reference numerals, and same descriptions being omitted.

In the present embodiment, the reference numerals 80A, 80B, and 80Crepresent liquid storage containers to which the refrigerator units 10A,10B, and 10C are attached, while 82A, 82C and 82B represent gas lines.The temperature sensors 24A, 24B, and 24C are not absolutely necessaryto be attached to first-stage or second-stage thermal-load portions ofthe refrigerator units, but can be attached to any desired positions ofthe simple liquefaction apparatuses.

According to the present embodiment, as described in the thirdembodiment, it is possible not only to adjust the temperatures of therespective refrigerators by the inverters 22A, 22B, and 22C provided inthe respective refrigerator units and to eliminate an irregularity amongthe refrigerator units, but also to reduce power consumption by thesecond inverter 40 provided in the compressor unit 30.

In the present embodiment, instead of using temperature sensors 24A,24B, and 24C, it is possible to install liquid-level sensors 28A, 28B,and 28C in the liquid storage containers 80A, 80B, and 80C and perform acontrol according to the outputs of the liquid-level sensors, as in aninth embodiment shown in FIG. 10, thereby obtaining the same effect asin the third embodiment.

Incidentally, although in the present embodiment the simple liquefactionapparatuses and the refrigerator units are combined with each other inone-to-one relation, it is also possible for the present embodiment tobe applied to a system in which a plurality of refrigerator units areused with a single simple liquefaction apparatus. Moreover, it ispossible to apply herein the first embodiment, the second embodiment,and the fourth embodiment.

Although each of the above-described embodiments shows that the presentinvention can be applied to control second-stage G-M cycle refrigerator,the present invention is not limited to such an application, and it isobvious that the present invention can be similarly applied to controlthe temperature of refrigerating machine in general (such as first-stageG-M cycle refrigerator, three-stage G-M cycle refrigerator, modifiedSolvay cycle refrigerator, pulse tube type refrigerator, etc.).Moreover, mechanism for managing the intake/exhaust cycle time is notlimited to the motor for driving an intake/exhaust valve.

INDUSTRIAL APPLICABILITY

According to the present invention, since the inverter and thecontroller constituting a temperature control mechanism are in a roomtemperature area, it is possible to adjust the temperature ofrefrigerator by a method having a higher reliability than that using anelectric heater provided in a low temperature unit. Moreover, even whena plurality of refrigerator units are operated by one or more compressorunits, it is still possible to adjust the temperatures of the respectiverefrigerator units, thereby eliminating an irregularity among therefrigerator units.

In particular, when inverter control of compressor unit is incorporated,it is possible for the system to adjust the rotation speed of compressorso as to obtain an optimum gas flow rate, thereby reducing powerconsumption.

1. A refrigerator unit characterized by comprising: means, which isprovided between a power source and a motor for driving anintake/exhaust valve managing an intake/exhaust cycle time of arefrigerator unit, for varying a frequency of the motor for driving theintake/exhaust valve; a temperature sensor for detecting a temperatureof a thermal load unit of the refrigerator unit; and a controller forcontrolling the means for varying the frequency of the motor for drivingthe intake/exhaust valve in accordance with an output signal of thetemperature sensor.
 2. A cryopump characterized by comprising therefrigerator unit according to claim
 1. 3. A cryogenic refrigeratorcharacterized by using a compressor unit comprising: means, which isprovided between a power source and a compressor main body motor of thecompressor unit, for varying a frequency of the compressor main bodymotor; a high pressure sensor attached to a high pressure refrigerantpipe connecting an outlet of the compressor main body with a refrigerantsupply port of the refrigerator unit; a low pressure sensor attached toa low pressure refrigerant pipe connecting an inlet of the compressormain body with a refrigerant discharge outlet of the refrigerator unit;a controller for controlling the means for varying the frequency of thecompressor main body motor in accordance with output signals of the highpressure sensor and the low pressure sensor, and characterized in that aplurality of the refrigerator units according to claim 1 and one or moreof the compressor units constitute the cryogenic refrigerator.
 4. Acryogenic refrigerator characterized by using a compressor unitcomprising: means, which is provided between a power source and acompressor main body motor of the compressor unit, for varying afrequency of the compressor main body motor; a differential pressuresensor provided between a high pressure refrigerant pipe connecting anoutlet of the compressor main body with a refrigerant supply port of therefrigerator unit and a low pressure refrigerant pipe connecting aninlet of the compressor main body with a refrigerant discharge outlet ofthe refrigerator unit; a controller for controlling the means forvarying the frequency of the compressor main body motor in accordancewith an output signal of the differential pressure sensor, andcharacterized in that a plurality of the refrigerator units according toclaim 1 and one or more of the compressor units constitute the cryogenicrefrigerator.
 5. A cryopump characterized by comprising the cryogenicrefrigerator according to claim 3 or
 4. 6. The cryopump according toclaim 5, comprising: a temperature sensor for detecting a temperature atany optional position of a cryopanel of the cryopump; and a controllerfor controlling the means for varying the frequency of the motor drivingthe intake/exhaust valve managing the intake/exhaust cycle time of therefrigerator unit in accordance with an output of the temperaturesensor.
 7. A superconductive magnet characterized by comprising therefrigerator unit according to claim
 1. 8. A super conductive magnetcharacterized by comprising the cryogenic refrigerator according toclaim 3 or
 4. 9. The superconductive magnet according to claim 7,comprising: a temperature sensor for detecting a temperature of anyoptional position of the superconductive magnet; and a controller forcontrolling the means for varying the frequency of the motor driving theintake/exhaust valve managing the intake/exhaust cycle time of therefrigerator unit in accordance with an output of the temperaturesensor.
 10. A cryogenic measuring apparatus characterized by comprisingthe refrigerator unit according to claim
 1. 11. A cryogenic measuringapparatus characterized by comprising the cryogenic refrigeratoraccording to claim 3 or
 4. 12. The cryogenic measuring apparatusaccording to claim 10, characterized by comprising a temperature sensorfor detecting a temperature of any optional position of the cryogenicmeasuring apparatus; and a controller for controlling the means forvarying the frequency of the motor driving the intake/exhaust valvemanaging the intake/exhaust cycle time of the refrigerator unit inaccordance with an output of the temperature sensor.
 13. A simpleliquefaction apparatus characterized by comprising the refrigerator unitaccording to claim
 1. 14. Currently Amended) A simple liquefactionapparatus characterized by comprising the cryogenic refrigeratoraccording to claim 3 or
 4. 15. The simple liquefaction apparatusaccording to claim 13, comprising: a temperature sensor for detecting atemperature of any optional position of the simple liquefactionapparatus; and a controller for controlling the means for varying thefrequency of the motor driving the intake/exhaust valve managing theintake/exhaust cycle time of the refrigerator unit in accordance with anoutput of the temperature sensor.
 16. The simple liquefaction apparatusaccording to claim 13, comprising: liquid-level detecting means within aliquid storage container of the simple liquefaction apparatus; and acontroller for controlling means for varying a frequency of a motordriving an intake/exhaust valve managing a intake/exhaust cycle time ofa refrigerator unit in accordance with an output of the liquid-leveldetecting means.